Atmospheric methylchloride (CH3Cl)

A global time series of atmospheric methylchloride (CH₃Cl) concentrations is reported showing the variability with latitude and season. Springtime concentrations of CH₃Cl at 45°N latitude are 7.5%±3.5% higher than during other seasons. Lowest concentrations were generally observed during fall. CH₃Cl was found to be more abundant by about 6% (±5% NH, ±3% SH) in the tropical regions of both hemispheres. No significant difference in the burdens of CH₃Cl was observed between the two hemispheres. Based on these data the ratio of the average hydroxyl radical (HO) concentration over the southern hemisphere to that over the northern hemisphere was estimated to be 1.3 or less.     

Latitudinal distributions of trace gases in and above the boundary layer

Statistical analyses of global atmospheric concentrations provide evidence that C₂Cl₄, CHCl₃ and CH₃CCl₃ (methylchloroform) are more abundant in the tropical boundary layer than above it (α ? 0.09) by 27% (±27%), 21% (?21%, +12%) and 6.4% (±6%) respectively. The air samples on which these results are based were collected by cryogenic techniques during the June 1978 project GAMETAG flights and analyzed soon afterwards by gas chromatography (EC/GC and GC/FID), thus providing latitudinal concentrations of CO, CH₄, CCl₃F, CCl₂F₂, CH₃CCl₃ and light C₂-hydrocarbons, both in and above the boundary layer. In August 1980, after further development of analytical techniques, the stored air samples were re-analyzed to establish the latitudinal distributions of CH₃I, CHCl₃, C₂Cl₄, C₂F₃Cl₃ (F-113) and CHClF₂ (F-22) in and above the boundary layer. Stability studies, spanning a year, show that the concentrations of these gases do not change in the flasks.     

Atmospheric alcohols and aldehydes concentrations measured in Osaka,Japan and in Sao Paulo,Brazil

The use of alcohol fuel has received much attention since 1980s. In Brazil, ethanol-fueled vehicles have been currently used on a large scale. This paper reports the atmospheric methanol, ethanol and isopropanol concentrations which were measured from May to December 1997, in Osaka, Japan, where alcohol fuel was not used, and from 3 to 9 February 1998, in Sao Paulo, Brazil, where ethanol fuel was used. The alcohols were determined by the alkyl nitrite formation reaction using gas chromatography (GC-ECD) analysis. The concentration of atmospheric alcohols, especially ethanol, measured in Sao Paulo were significantly higher than those in Osaka. In Osaka, the average concentrations of atmospheric methanol, ethanol, and isopropanol were 5.8±3.8, 8.2±4.6, and 7.2±5.9 ppbv, respectively. The average ambient levels of methanol, ethanol, and isopropanol measured in Sao Paulo were 34.1±9.2, 176.3.±38.1, and 44.2±13.7 ppbv, respectively. The ambient levels of aldehydes, which were expected to be high due to the use of alcohol fuel, were also measured at these sampling sites. The atmospheric formaldehyde average concentration measured in Osaka was 1.9±0.9 ppbv, and the average acetaldehyde concentration was 1.5±0.8 ppbv. The atmospheric formaldehyde and acetaldehyde average concentrations measured in Sao Paulo were 5.0±2.8 and 5.4±2.8 ppbv, respectively. The C₂H₅OH/CH₃OH and CH₃CHO/HCHO were compared between the two measurement sites and elsewhere in the world, which have already been reported in the literature. Due to the use of ethanol-fueled vehicles, these ratios, especially C₂H₅OH/CH₃OH, are much higher in Brazil than these measured elsewhere in the world.     

Rate Constants for the Reaction of OH with Halocarbons in the Presence of O2 + N2

Rates of CO₂ production in the reaction CO + OH and CO + OH + halocarbon have been used to determine rate constants for some OH + halocarbon reactions at 29.5°C relative to that of k(CO + OH) = 2.69 × 10^?13 cm³ molecule^?1 sec^?1. The following rate constants were obtained: k(OH + CH₃Cl) = 3.1 ± 0.8, k(OH + CH₂Cl₂) = 2.7 ± 1.0, k(OH + C₂H₅Cl) = 44.0 ± 25, k(OH + CICH₂CH₂CI) = 6.5, (<29) and k(OH + CH₃CCl₃) = 2.1 (<5.7) cm³ molecule^?1 sec^?1 × 10^?14. The k values, CH₂Cl₂ excepted, are in substantial agreement with determinations made in nonoxygen environments. The present results for CH₂Cl₂ are almost certainly in error due to difficulties with the competitive approach used.     

The use of CFC-12, CFC-11 and CH3CCl3 to trace terrestrial airborne pollutant transport by land–sea breezes

Time-series observations of the atmospheric concentrations of the halocarbons, trichlorofluorocarbon (CFC-11), dichlorofluorocarbon (CFC-12), 1,2-trichlorofluoroethane (CFC-113), methyl chloroform (CH₃CCl₃) and carbon tetrachloride (CCl₄) were conducted at a site in Lukang, in Central Taiwan between April and August 2004. Fluctuations in atmospheric concentrations of CFC-11, CFC-12 and CH₃CCl₃ were generally driven by diurnal land–sea breeze and anthropogenic activity in this area. Elevated levels of CFC-11, CFC-12, and CH₃CCl₃ frequently occurred when the air was stagnant and the prevailing seaward land breeze was dominant. Atmospheric concentrations of CFC-113 and CCl₄ were much less variable relative to CFC-11, CFC-12 and CH₃CCl₃ during the same period, indicating that emissions of these two species from anthropogenic activities were small. The time-series distributions of atmospheric levels of CFC-12, CFC-11, CH₃CCl₃ and CO were characterized as a diurnal cycle with an elevated level at night and a low level during the daytime for most of the observed periods. As CFC-12, CFC-11 and CH₃CCl₃ behave as traffic- and industry-derived airborne pollutants in the urban atmosphere, they provide as a useful tracer in the application for the study of terrestrial airborne pollutants transport across the coastal area driven by land–sea breezes in this area.     

Major air pollutants in Bursa,Turkey: their levels,temporal changes,interactions, and sources

Bursa is one of the largest cities of Turkey and it hosts 17 organized industrial zones. Parallel to the increase in population, rapidly growing energy consumption, and increased numbers of transport vehicles have impacts on the air quality of the city. In this study, regularly calibrated automatic samplers were employed to get the levels of air pollution in Bursa. The concentrations of CH₄ and N-CH₄ as well as the major air pollutants including PM₁₀, PM_2.5, NO, NO₂, NO_x, SO₂, CO, and O₃, were determined for 2016 and 2017 calendar years. Their levels were 1641.62?±?718.25, 33.11?±?5.45, 42.10?±?10.09, 26.41?±?9.01, 19.47?±?16.51, 46.73?±?16.56, 66.23?±?32.265, 7.60?±?3.43, 659.397?±?192.73, and 51.92?±?25.63 µg/m³ for 2016, respectively. Except for O₃, seasonal concentrations were higher in winter and autumn for both years. O₃, CO, and SO₂ had never exceeded the limit values specified in the regulations yet PM₁₀, PM_2.5, and NO₂ had violated the limits in some days. The ratios of CO/NO_x, SO₂/NO_x, and PM_2.5/PM₁₀ were examined to characterize the emission sources. Generally, domestic and industrial emissions were dominated in the fall and winter seasons, yet traffic emissions were effective in spring and summer seasons. As a result of the correlation process between O_x and NO_x, it was concluded that the most important source of O_x concentrations in winter was NO_x and O₃ was in summer.     

Secular trends of atmospheric methane (CH4)

Due partly to human activities the present yearly emissions of CH₄ exceed the atmospheric sinks, thus leading to a 1.2–1.9% per year atmospheric increase in the concentration of CH₄. New evidence based on studies of polar ice cores suggests that several hundred years ago the concentrations of CH₄ were perhaps only half of current values. These diverse findings are tied together in a single unified logistic model of atmospheric concentrations past, present and future. Using realistic growth rates of the sources of CH₄ caused by human activities, the model explains the concentrations and current growth rates. It also predicts that a doubling of CH₄ relative to present levels is possible given the long (9-year) atmospheric lifetime. Such increases of CH₄ concentrations may have already perturbed our global environment and may continue to do so in the future. The environmental effects include increased surface temperature of the earth, additional O₃ and CO in the clean non-urban atmosphere, depletions of tropospheric OH radicals, but perhaps also protection of the stratospheric ozone layer from destruction by man-made fluorocarbons.     

FTIR gas-phase kinetic study on the reactions of some acrylate esters with OH radicals and Cl atoms

Acrylate esters are α,β-unsaturated esters that contain vinyl groups directly attached to the carbonyl carbon. These compounds are widely used in the production of plastics and resins. Atmospheric degradation processes of these compounds are currently not well understood. The kinetics of the gas phase reactions of OH radicals with methyl 3-methylacrylate and methyl 3,3-dimethylacrylate were determined using the relative rate technique in a 50 L Pyrex photoreactor using in situ FTIR spectroscopy at room temperature (298?±?2 K) and atmospheric pressure (708?±?8 Torr) with air as the bath gas. Rate coefficients obtained were (in units cm³ molecule^?1 s^?1): (3.27?±?0.33)?×?10^?11 and (4.43?±?0.42)?×?10^?11, for CH₃CH═CHC(O)OCH₃ and (CH₃)₂CH═CHC(O)OCH_3, respectively. The same technique was used to study the gas phase reactions of hexyl acrylate and ethyl hexyl acrylate with OH radicals and Cl atoms. In the experiments with Cl, N₂ and air were used as the bath gases. The following rate coefficients were obtained (in cm³ molecule^?1 s^?1): k₃ (CH₂═CHC(O)O(CH₂)₅CH₃?+?Cl)?=?(3.31?±?0.31)?×?10^?10, k₄(CH₂═CHC(O)OCH₂CH(CH₂CH₃)(CH₂)₃CH₃?+?Cl)?=?(3.46?±?0.31)?×?10^?10, k₅(CH₂═CHC(O)O(CH₂)₅CH₃?+?OH)?=?(2.28?±?0.23)?×?10^?11, and k₆(CH₂═CHC(O)OCH₂CH(CH₂CH₃)(CH₂)₃CH₃?+?OH)?=?(2.74?±?0.26)?×?10^?11. The reactivity increased with the number of methyl substituents on the double bond and with the chain length of the alkyl group in –C(O)OR. Estimations of the atmospheric lifetimes clearly indicate that the dominant atmospheric loss process for these compounds is their daytime reaction with the hydroxyl radical. In coastal areas and in some polluted environments, Cl atom-initiated degradation of these compounds can be significant, if not dominant. Maximum Incremental Reactivity (MIR) index and global warming potential (GWP) were also calculated, and it was concluded that these compounds have significant MIR values, but they do not influence global warming.     

The rate and mechanism of the gas-phase oxidation of hydroxyacetone

The rate and mechanism for gas-phase destruction of hydroxyacetone, CH₃C(O)CH₂OH, by reaction with OH, Cl-atoms, and by photolysis have been determined. The first quantitative UV absorption spectrum of hydroxyacetone is reported over the wavelength range 235 to 340 nm; the spectrum is blue-shifted by about 15 nm relative to that of acetone and peaks at 266 nm, with a maximum absorption cross section of (6.7±0.6) ×10^-20 cm² molecule^-1. Measurable absorption extends out to about 330 nm. The quantum yield for photolysis of hydroxyacetone in the region relevant to the troposphere (λ>290 nm) was found to be significantly less than unity. Rate coefficients for the reaction of hydroxyacetone with OH radicals and Cl-atoms were determined at 298 K using the relative rate technique. The rate coefficient for reaction with OH was found to be (3.0±0.7)×10^-12 cm³ molecule^-1 s^-1, while the rate coefficient for reaction with Cl-atoms was found to be (5.6±0.7)×10^-11 cm³ molecule^-1 s^-1. Both values agree well with previous studies. The data were used to determine the lifetime of hydroxyacetone in the troposphere. Reaction with OH is the major gas-phase destruction mechanism for this compound, limiting its lifetime to about 4 days, while photolysis is found to be only of minor importance.     

Tropospheric halocompounds and nitrous oxide monitored at a remote site in the Mediterranean

Analysis of time series and trends of nitrous oxide (N₂O) and halocompounds weekly monitored at the Mediterranean island of Lampedusa are discussed. Atmospheric N₂O levels showed a linear upward growth rate of 0.78 ppb yr^?1 and mixing ratios comparable with Northern Hemisphere global stations. CFC-11 and CFC-12 time series displayed a decline consistent with their phase-out. Chlorofluorocarbons (CFCs) replacing compounds and SF₆ exhibited an increasing temporal behaviour. The most rapid growth rate was recorded for HFC-134a with a value of 9.6% yr^?1. The industrial solvents CCl₄ and CH₃CCl₃, banned by the Montreal Protocol, showed opposite trends. While CH₃CCl₃ reported an expected decay of ?1.8 ppt yr^?1, an increasing rate of 5.7 ppt yr^?1 was recorded for CCl₄ and it is probably related to its relatively long lifetime and persisting emissions. Chlorinated halomethanes showed seasonality with a maximum in early April and a minimum at the end of September. Halon-1301 and Halon-1211 displayed a decreasing trend consistent with industry emission estimates.An interspecies correlation analysis gave positive high correlations between HCFC-22 and HFC-134a (+0.84) highlighting the common extensive employment as refrigerants. Sharing sources inferred the high coupling between CH₃Cl and CH₃Br (+0.73) and between CHCl₃ and CH₂Cl₂ (+0.77). A singular strong relationship (+0.55) between HFC-134a and CH₃I suggested the influence of an unknown anthropogenic source of CH₃I.Constraining of source and sink distribution was carried out by transport studies. Results were compared with the European Environment Agency (EEA) emission database. In contrast with the emission database results, our back trajectory analysis highlighted the release of large amounts of HFC-134a and SF₆ from Eastern Europe. Observations also showed that African SF₆ emissions may be considerable. Leakages from SF₆ insulated electrical equipments located in the industrialized Northern African areas justify our observations.     

A PLP–LIF kinetic study of the atmospheric reactivity of a series of C4–C7 saturated and unsaturated aliphatic aldehydes with OH

Absolute rate coefficients for the reaction of OH radical with a series of saturated and unsaturated aliphatic aldehydes were measured with the pulsed laser photolysis/laser-induced fluorescence technique at room temperature and as a function of total pressure (p_T=100–400 Torr). No pressure dependence of the rate coefficients was observed. The weighted average values obtained, k_OH±2σ, in units of 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, were 2.88±0.26 for n-butanal, 2.48±0.24 for n-pentanal, 2.60±0.21 for n-hexanal, 2.96±0.23 for n-heptanal, 3.51±0.71 for crotonaldehyde, 2.35±0.32 for trans-2-pentenal, 2.95±0.45 for trans-2-hexenal and 2.45±0.30 for trans-2-heptenal, respectively. The results are compared with previous data when available and with the corresponding coefficients for the reactions with NO₃ and O₃. The dominant tropospheric chemical loss process for these aliphatic aldehydes is the daytime reaction with OH, except in the case of trans-2-heptenal where the estimated lifetime for the reaction with NO₃ radical is smaller than the corresponding value for the OH reaction.     

Temperature-dependent rate coefficients for the reactions of Cl atoms with methyl methacrylate,methyl acrylate and butyl methacrylate at atmospheric pressure

Rate coefficients for the gas-phase reactions of Cl atoms with a series of unsaturated esters CH₂C(CH₃)C(O)OCH₃ (MMA), CH₂CHC(O)OCH₃ (MAC) and CH₂C(CH₃)C(O)O(CH₂)₃CH₃ (BMA) have been measured as a function of temperature by the relative technique in an environmental chamber with in situ FTIR detection of reactants. The rate coefficients obtained at 298 K in one atmosphere of nitrogen or synthetic air using propene, isobutene and 1,3-butadiene as reference hydrocarbons were (in units of 10^?10 cm³ molecule^?1 s^?1) as follows: k_(Cl+MMA) = 2.82 ± 0.93, k_(Cl+MAC) = 2.04 ± 0.54 and k_(Cl+BMA) = 3.60 ± 0.87. The kinetic data obtained over the temperature range 287–313 K were used to derive the following Arrhenius expressions (in units of cm³ molecule^?1 s^?1): k_(Cl+MMA) = (13.9 ± 7.8) × 10^?15 exp[(2904 ± 420)/T], k_(Cl+MAC) = (0.4 ± 0.2) × 10^?15 exp[(3884 ± 879)/T], k_(Cl+BMA) = (0.98 ± 0.42) × 10^?15 exp[(3779 ± 850)/T]. All the rate coefficients display a slight negative temperature dependence which points to the importance of the reversibility of the addition mechanism for these reactions. This work constitutes the first kinetic and temperature dependence study of the reactions cited above.An analysis of the available rates of addition of Cl atoms and OH radicals to the double bond of alkenes and unsaturated and oxygenated volatile organic compounds (VOCs) at 298 K has shown that they can be related by the expression: log k_OH = 1.09 log k_Cl ? 0.10. In addition, a correlation between the reactivity of unsaturated VOCs toward OH radicals and Cl atoms and the HOMO of the unsaturated VOC is presented. Tropospheric implications of the results are also discussed.     

Characterization of emissions from portable household combustion devices: particle size distributions,emission rates and factors,and potential exposures

A series of source tests were conducted to characterize emissions of particulate matter (PM), carbon monoxide (CO), carbon dioxide (CO₂), methane (CH₄), and total hydrocarbon (THC ) from five types of portable combustion devices. Tested combustion devices included a kerosene lamp, an oil lamp, a kerosene space heater, a portable gas range, and four unscented candles. All tests were conducted either in a well-mixed chamber or a well-mixed room, which enables us to determine emission rates and emission factors using a single-compartment mass balance model. Particle mass concentrations and number concentrations were measured using a nephelometric particle monitor and an eight-channel optical particle counter, respectively. Real-time CO concentrations were measured with an electrochemical sensor CO monitor. CO₂, CH₄, and THC were measured using a GC-FID technique. The results indicate that all particles emitted during steady burning in each of the tested devices were smaller than 1.0 μm in diameter with the vast majority in the range between 0.1 and 0.3 μm. The PM mass emission rates and emission factors for the tested devices ranged from 5.6±0.1 to 142.3±40.8 mg h⁻¹ and from 0.35±0.06 to 9.04±4.0 mg g⁻¹, respectively. The CO emission rates and emission factors ranged from 4.7±3.0 to 226.7±100 mg h⁻¹ and from 0.25±0.12 to 1.56±0.7 mg g⁻¹, respectively. The CO₂ emission rates and emission factors ranged from 5500±700 to 210,000±90,000 mg h⁻¹ and from 387±45 to 1689±640 mg g⁻¹, respectively. The contributions of CH₄ and THC to emission inventories are expected to be insignificant due both to the small emission factors and to the relatively small quantity of fuel consumed by these portable devices. An exposure scenario analysis indicates that every-day use of the kerosene lamp in a village house can generate fine PM exposures easily exceeding the US promulgated NAAQS for PM_2.5.     

Analysis of 3-year observations of CFC-11, CFC-12 and CFC-113 from a semi-rural site in China

In-situ measurements of atmospheric chlorofluorocarbons (CFCs) can be used to the assess their global and regional emissions and to check for compliance with phase-out schedules under Montreal protocol and its amendments. The atmospheric mixing ratios of CFC-11 (CCl₃F), CFC-12 (CCl₂F₂) and CFC-113 (CCl₂F–CClF₂) have been measured by an automated in-situ GC-ECDs system at the regional Chinese Global Atmosphere Watch (GAW) station Shangdianzi (SDZ), from November 2006 to October 2009. The time series for these three principal CFCs showed large episodic events and background conditions occurred for approximately 30% (CFC-11), 52% (CFC-12) and 56% (CFC-113) of the measurements. The mean background mixing ratios for CFC-11, CFC-12 and CFC-113 were 244.8 ppt (parts per trillion, 10^?12, molar) 539.6 ppt and 76.8 ppt, respectively, for 2006–2009. The enhanced CFC mixing ratios compared to AGAGE sites such as Trinidad Head (THD), US and Mace Head (MHD), Ireland suggest regional influences even during background conditions at SDZ, which is much closer to highly-populated areas. Between 2006 and 2009 background CFCs exhibited downward trends at rates of ?2.0 ppt yr^?1 for CFC-11, ?2.5 ppt yr^?1 for CFC-12 and ?0.7 ppt yr^?1 for CFC-113. De-trended 3-year average background seasonal cycles displayed small fluctuations with peak-to-trough amplitudes of 1.0 ± 0.02 ppt (0.4%) for background CFC-11, 1.3 ± 2.1 ppt (0.3%) for CFC-12 and 0.2 ± 0.4 ppt (0.3%) for CFC-113. On the other hand, during pollution periods these CFCs showed much larger seasonal cycles of 11.2 ± 10.7 ppt (5%) for CFC-11, 7.5 ± 6.5 ppt (2%) for CFC-12 and 1.0 ± 1.2 ppt (1.2%) for CFC-113, with apparent winter minima and early summer maxima. This enhancement was attributed to prevailing wind directions from urban regions in summer and to enhanced anthropogenic sources during the warm season. In general, horizontal winds from northeast showed negative contribution to atmospheric CFCs loading, whereas South Western advection (urban sector: Beijing) had positive contributions.     

Cyclooctane tropospheric degradation initiated by reaction with Cl atoms

Goal, Scope and Background Within the non-methane hydrocarbons, alkanes constitute the largest fraction of the anthropogenic emissions of volatile organic compounds. For the case of cyclic alkanes, tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase. Nevertheless, Cl atom reaction rate constants are generally one order of magnitude larger than those of OH. In the present work, the reaction of cyclooctane with Cl atoms has been studied within the temperature range of 279–333 K. Methods The kinetic study has been carried out using the fast flow tube technique coupled to mass spectrometry detection. The reaction has been studied under low pressure conditions, p=1 Torr, with helium as the carrier gas. Results The measured room temperature rate constant is very high, k=(2.63±0.54)×10⁻¹⁰ cm³molecule⁻¹s⁻¹, around 20 times larger than that for the corresponding OH reaction. We also report the results of the rate coefficients obtained at different temperatures: k = (3.5±1.2)×10⁻¹⁰ exp[(−79±110)/T] cm³ molecule⁻¹ s⁻¹ within the range of 279–333 K. This reaction shows an activation energy value close to zero. Discussion Quantitative formation of HCl has been observed, confirming the mechanism through H-atom abstraction. The reactivity of cyclic alkanes towards Cl atoms is clearly dependent on the number of CH₂ groups in the molecule, as is shown by the increase in the rate constant when the length of the organic chain increases. This increase is very high for the small cyclic alkanes and it seems that the reactions are approaching the collision-controlled limit for cyclohexane and cyclooctane. Conclusions These results show that gas-phase reaction with Cl in marine or coastal areas is an efficient sink (competing with the gas phase, OH initiated degradation) for the Earth’s emissions of cyclooctane, with a Cl-based lifetime ranging from 11 to 2000 hours, depending on the location and time of day. Recommendations and Perspectives Cl and OH fast reactions with cyclooctane are expected to define the lifetime of cyclooctane emissions to the atmosphere. The degradation of cyclooctane occurs in a short period of time and consequently (under conditions of low atmospheric mass transport), close to the emission sources enabling a significant contribution to local effects, like the formation of photochemical smog. ESS-Submission Editor: Prof. Dr. Gerhard Lammel (lammel@recetox.muni.cz)     

Atmospheric chemistry of HFE-7000 (CF(3)CF (2)CF (2)OCH (3)) and 2,2,3,3,4,4,4-heptafluoro-1-butanol (CF (3)CF (2)CF (2)CH (2)OH): kinetic rate coefficients and temperature dependence of reactions with chlorine atoms

Background, aim, and scope  The adverse environmental impacts of chlorinated hydrocarbons on the Earth’s ozone layer have focused attention on the effort to replace these compounds by nonchlorinated substitutes with environmental acceptability. Hydrofluoroethers (HFEs) and fluorinated alcohols are currently being introduced in many applications for this purpose. Nevertheless, the presence of a great number of C–F bonds drives to atmospheric long-lived compounds with infrared absorption features. Thus, it is necessary to improve our knowledge about lifetimes and global warming potentials (GWP) for these compounds in order to get a complete evaluation of their environmental impact. Tropospheric degradation is expected to be initiated mainly by OH reactions in the gas phase. Nevertheless, Cl atoms reaction may also be important since rate constants are generally larger than those of OH. In the present work, we report the results obtained in the study of the reactions of Cl radicals with HFE-7000 (CF₃CF₂CF₂OCH₃) (1) and its isomer CF₃CF₂CF₂CH₂OH (2). Materials and methods  Kinetic rate coefficients with Cl atoms have been measured using the discharge flow tube–mass spectrometric technique at 1 Torr of total pressure. The reactions of these chlorofluorocarbons (CFCs) substitutes have been studied under pseudo-first-order kinetic conditions in excess of the fluorinated compounds over Cl atoms. The temperature ranges were 266–333 and 298–353 K for reactions of HFE-7000 and CF₃CF₂CF₂CH₂OH, respectively. Results  The measured room temperature rate constants were k(Cl+CF₃CF₂CF₂OCH₃) = (1.24 ± 0.28) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹and k(Cl+CF₃CF₂CF₂CH₂OH) = (8.35 ± 1.63) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ (errors are 2σ + 10% to cover systematic errors). The Arrhenius expression for reaction 1 was k ₁(266–333 K) = (6.1 ± 3.8) × 10⁻¹³exp[−(445 ± 186)/T] cm³ molecule⁻¹ s⁻¹ and k ₂(298–353 K) = (1.9 ± 0.7) × 10⁻¹²exp[−(244 ± 125)/T] cm³ molecule⁻¹ s⁻¹ (errors are 2σ). The reactions are reported to proceed through the abstraction of an H atom to form HCl and the corresponding halo-alkyl radical. At 298 K and 1 Torr, yields on HCl of 0.95 ± 0.38 and 0.97 ± 0.16 (errors are 2σ) were obtained for CF₃CF₂CF₂OCH₃ and CF₃CF₂CF₂CH₂OH, respectively. Discussion  The obtained kinetic rate constants are related to the previous data in the literature, showing a good agreement taking into account the error limits. Comparing the obtained results at room temperature, k ₁ and k ₂, HFE-7000 is significantly less reactive than its isomer C₃F₇CH₂OH. A similar behavior has been reported for the reactions of other fluorinated alcohols and their isomeric fluorinated ethers with Cl atoms. Literature data, together with the results reported in this work, show that, for both fluorinated ethers and alcohols, the kinetic rate constant may be considered as not dependent on the number of –CF₂– in the perfluorinated chain. This result may be useful since it is possible to obtain the required physicochemical properties for a given application by changing the number of –CF₂– without changes in the atmospheric reactivity. Furthermore, lifetimes estimations for these CFCs substitutes are calculated and discussed. The average estimated Cl lifetimes are 256 and 38 years for HFE-7000 and C₃H₇CH₂OH, respectively. Conclusions  The studied CFCs’ substitutes are relatively short-lived and OH reaction constitutes their main reactive sink. The average contribution of Cl reactions to global lifetime is about 2% in both cases. Nevertheless, under local conditions as in the marine boundary layer, τ _Cl values as low as 2.5 and 0.4 years for HFE-7000 and C₃H₇CH₂OH, respectively, are expected, showing that the contribution of Cl to the atmospheric degradation of these CFCs substitutes under such conditions may constitute a relevant sink. In the case of CF₃CF₂CF₂OCH₃, significant activation energy has been measured, thus the use of kinetic rate coefficient only at room temperature would result in underestimations of lifetimes and GWPs. Recommendations and perspectives  The results obtained in this work may be helpful within the database used in the modeling studies of coastal areas. The knowledge of the atmospheric behavior and the structure–reactivity relationship discussed in this work may also contribute to the development of new environmentally acceptable chemicals. New volatile materials susceptible of emission to the troposphere should be subject to the study of their reactions with OH and Cl in the range of temperature of the troposphere. The knowledge of the temperature dependence of the kinetic rate constants, as it is now reported for the case of reactions 1 and 2, will allow more accurate lifetimes and related magnitudes like GWPs. Nevertheless, a better knowledge of the vertical Cl tropospheric distribution is still required.     

Measurement and Analysis of the Relationship between Ammonia,Acid Gases,and Fine Particles in Eastern North Carolina

Abstract

An annular denuder system, which consisted of a cyclone separator; two diffusion denuders coated with sodium carbonate and citric acid, respectively; and a filter pack consisting of Teflon and nylon filters in series, was used to measure acid gases, ammonia (NH₃), and fine particles in the atmosphere from April 1998 to March 1999 in eastern North Carolina (i.e., an NH₃?rich environment). The sodium carbonate denuders yielded average acid gas concentrations of 0.23 μg/m³ hydrochloric acid (standard deviation [SD] ± 0.2 μg/m³); 1.14 μg/m³ nitric acid (SD ± 0.81 μg/m³), and 1.61 μg/m³ sulfuric acid (SD ± 1.58 μg/m³). The citric acid denuders yielded an average concentration of 17.89 μg/m³ NH₃ (SD ± 15.03 μg/m³). The filters yielded average fine aerosol concentrations of 1.64 μg/m³ ammonium (NH₄ ⁺;SD ± 1.26 μg/m³); 0.26 μg/m³ chloride (SD ± 0.69 μg/m³), 1.92 μg/m³ nitrate (SD ± 1.09 μg/m³), and 3.18 μg/m³ sulfate (SO₄ ^2?; SD ± 3.12 μg/m³). From seasonal variation, the measured particulates (NH₄ ⁺,SO₄ ^2?, and nitrate) showed larger peak concentrations during summer, suggesting that the gas-to-particle conversion was efficient during summer. The aerosol fraction in this study area indicated the domination of ammonium sulfate particles because of the local abundance of NH₃, and the long-range transport of SO₄ ^2? based on back trajectory analysis. Relative humidity effects on gas-to-particle conversion processes were analyzed by particulate NH₄ ⁺ concentration originally formed from the neutralization processes with the secondary pollutants in the atmosphere.     

Atmospheric fate of acrylic acid and acrylonitrile: Rate constants with Cl atoms and OH radicals in the gas phase

Rate coefficients for the reactions of hydroxyl radicals and chlorine atoms with acrylic acid and acrylonitrile have been determined at 298 K and atmospheric pressure. The decay of the organics was followed using a gas chromatograph with a flame ionization detector (GC-FID) and the rate constants were determined using a relative rate method with different reference compounds. Room temperature rate constants are found to be (in cm³ molecule⁻¹ s⁻¹): k₁(OH+CH₂CHC(O)OH)=(1.75±0.47)×10⁻¹¹, k₂(Cl+CH₂CHC(O)OH)=(3.99±0.84)×10⁻¹⁰, k₃(OH+CH₂CHCN)=(1.11±0.33)×10⁻¹¹ and k₄(Cl+CH₂CHCN)=(1.11±0.23)×10⁻¹⁰ with uncertainties representing ±2σ. This is the first kinetic study for these reactions under atmospheric pressure. The rate coefficients are compared with previous determinations taking into account the effect of pressure on the rate constants. The effect of substituent atoms or groups on the overall rate constants is analyzed in comparison with other unsaturated compounds in the literature. In addition, atmospheric lifetimes based on the homogeneous sinks of acrylic acid and acrylonitrile are estimated and compared with other tropospheric sinks for these compounds.     

Photochemistry of phenanthrene,pyrene, and fluoranthene in ice and snow

Although polycyclic aromatic hydrocarbons (PAHs) are common pollutants in snow, there is little quantitative data about their rates of photodegradation in this environment. To begin to address this gap, we have measured the degradation kinetics of phenanthrene, pyrene, and fluoranthene on ice, as these are the most abundant PAHs in arctic snow. Frozen aqueous solutions of individual PAHs, with and without added hydrogen peroxide (HOOH) as a source of hydroxyl radical (OH), were illuminated with simulated sunlight. For all three PAHs, direct photodecay is the main mechanism of degradation, while OH-initiated indirect photodegradation is a minor sink. Rate constants (±1 SE) for direct photodegradation extrapolated to midday, surface snow conditions at Summit, Greenland on the summer solstice are 3.8 (±0.8) × 10^?5, 28 (±3) × 10^?5, and 1.4 (±0.7) × 10^?5 s^?1 for phenanthrene, pyrene, and fluoranthene, respectively. Apparent quantum efficiencies for photodegradation with simulated sunlight were 3.8 (±0.8) × 10^?3, 4.3 (±0.5) × 10^?4, and 2 (±1) × 10^?5, respectively. Calculated PAH lifetimes in surface snow under Summit conditions are 1–19 h during mid-summer, but increase to >100 days in the dark winter. While the short photodegradation lifetimes in the summer suggest that there should be no appreciable PAH levels in this season, past measurements at Summit sometimes show significant levels of these PAHs in summer surface snow. This discrepancy is likely due to differences in PAH location between lab samples (where the PAHs are probably in quasi-liquid layers) and real snow (where PAHs are likely primarily associated with particulate matter).     

Atmospheric chemistry of 1-methyl-2-pyrrolidinone

Rate constants for the atmospheric reactions of 1-methyl-2-pyrrolidinone with OH radicals, NO₃ radicals and O₃ have been measured at 296±2 K and atmospheric pressure of air, and the products of the OH radical and NO₃ radical reactions investigated. Using relative rate techniques, rate constants for the gas-phase reactions of OH and NO₃ radicals with 1-methyl-2-pyrrolidinone of (2.15±0.36)×10^-11 cm³ molecule^-1 s^-1 and (1.26±0.40)×10^-13 cm³ molecule^-1 s^-1, respectively, were measured, where the indicated errors include the estimated overall uncertainties in the rate constants for the reference compounds. An upper limit to the rate constant for the O₃ reaction of <1×10^-19 cm³ molecule^-1 s^-1 was also determined. These kinetic data lead to a calculated tropospheric lifetime of 1-methyl-2-pyrrolidinone of a few hours, with both the daytime OH radical reaction and the nighttime NO₃ radical reaction being important loss processes. Products of the OH radical and NO₃ radical reactions were analyzed by gas chromatography with flame ionization detection and combined gas chromatography–mass spectrometry. N-methylsuccinimide and (tentatively) 1-formyl-2-pyrrolidinone were identified as products of both of these reactions. The measured formation yields of N-methylsuccinimide and 1-formyl-2-pyrrolidinone were 44±12% and 41±12%, respectively, from the OH radical reaction and 59±16% and ∼4%, respectively, from the NO₃ radical reaction. Reaction mechanisms consistent with formation of these products are presented.